1. Field of the Invention
The present invention relates to a blood collecting tube and, more particularly, an evacuated blood collecting tube with an improved sealing assembly capable of being easily fitted to a bottom-closed tubular member and having a low resistance to insertion and removal of a piercing needle for collection of a blood sample.
2. Description of Related Art
In the medical field, evacuated blood collecting tubes are widely used to collect blood samples from patients. The blood collecting tube generally comprises a bottom-closed tubular member, i.e., a tubular member closed at one end and open at the other end, which is evacuated and sealed by a stopper fitted in the open end of the tubular member to retain its vacuum. Such tubular members are made of glass at the beginning, but the most of recent tubular members are made of synthetic resins as the glass tubes are easy to break and cause the problem of waste disposal. Such blood collecting tubes are disclosed, for example, in U.S. Pat. Nos. 3,734,080 and 3,890,955, and Japanese patent publication No. Heisei 2-49099.
The blood collecting tubes widely used include a bottom-closed tubular member made of synthetic resins having a small gas-permeability or a good gas-barrier property, such as polyethylene terephthalate for example, the tubular member being evacuated and closed by fitting a stopper made of elastomeric material such as butyl rubber or natural rubber in the open end of the tubular member under a reduced pressure. However, such blood collecting tubes have such a disadvantage that the quality deteriorates gradually during storage as gases such as air diffuses through the tubular member and stopper and causes lowering of the degree of vacuum in the evacuated tube. Thus, there is an increasing demand for evacuated blood collecting tubes with good quality.
Further, the above blood collecting tubes include the following problems as the stopper is held in place by frictional resistance between an annular outer surface of the stopper and an annular inner surface of the evacuated tube. For example, when collecting blood samples from a patient, it is common practice to use the evacuated blood collecting tube in combination with a holder having a double ended cannula of which one end is adapted to be pierced into a blood vessel while the other end is adapted to be penetrated into the stopper. In this case, blood samples are collected by first piercing one end of the cannula of the holder into a blood vessel of the patient, inserting the other end of the cannula into the tube through a diaphragm portion of the stopper, removing the cannula from the blood vessel, and then removing the holder from the blood collecting tube containing a collected blood sample.
Since the stopper possesses a large resistance to insertion of cannula, it is required to use a large-sized cannula to prevent it from bending during insertion of the cannula into the stopper. The greater the diameter of cannula, the greater the resistance to insertion and removal of the cannula. Thus, there is fear that the stopper may slip out of the tube at the time of removal of the holder if the frictional resistance between the stopper and cannula is greater than the frictional resistance between the tubular member and stopper. Further, the use of a large-sized cannula would load the patient at the time of collection of blood samples.
In addition, the rubber stopper removed from the tubular member is occasionally reused to close the open end of the tubular member. In this case, the insertion of the stopper causes compression of air in the bottom-closed tubular member, which causes a phenomenon that the stopper hops up.
On the other hand, if the above blood collecting tubes are used to supply the blood samples to an automatic blood analyzer having a hollow needle for taking blood samples from the tube, the rubber stopper occasionally comes off as the frictional resistance between the stopper and the needle pierced therein exceeds the frictional resistance between the tubular member and the stopper, resulting in leakage of the blood sample in the analyzer.
Japanese patent publication No. Heisei 2-25611 (corresponding to U.S. Pat. No. 4,465,200) discloses a blood collecting tube with an improved closure assembly comprising an annular stopper body with an upper outwardly extending annular flange portion and a lower annular skirt portion, and a flexible cap body for mounting on the annular stopper body. This closure assembly makes it possible to reduce the incidence of contamination of the user of the evacuated tube, but it includes problems similar to those disclosed in the aforesaid U.S. patents.
Japanese patent unexamined publication No. Heisei 2-212768 discloses a blood collecting tube of a thin film type composed of a tubular member closed at one end and open at the other end, a cap member removably fitted on the open end of the tubular member with a threaded structure, and a sealing member arranged between the cap member and the open end of the tubular member to seal the opening of the tubular member, said sealing member having a gas barrier film such as an aluminum laminated film and a re-sealing member made of natural rubber and bonded to the gas barrier film member in an overlapped relation. The blood collecting tube of the kind has various advantages, but it is impossible to remove the sealing member and cap member with one hand as the cap is screw-mounted on the tubular member.